Method setlistdefault

src/werkzeug/datastructures/headers.py:449–466

Return the list of values for the key if it is in the headers, otherwise set the header to the list of values given by ``default`` and return that. Unlike :meth:`MultiDict.setlistdefault`, modifying the returned list will not affect the headers. :param key:

(self, key: str, default: cabc.Iterable[t.Any])

        return self._get_key(key)

    def setlistdefault(self, key: str, default: cabc.Iterable[t.Any]) -> list[str]:
        """Return the list of values for the key if it is in the
        headers, otherwise set the header to the list of values given
        by ``default`` and return that.

        Unlike :meth:`MultiDict.setlistdefault`, modifying the returned
        list will not affect the headers.

        :param key: The header key to get.
        :param default: An iterable of values to set for the key if it
            is not in the headers.

        .. versionadded:: 1.0
        """
        if key not in self:
            self.setlist(key, default)

        return self.getlist(key)

    @t.overload
    def __setitem__(self, key: str, value: t.Any) -> None: ...